Hollow bodies, tubular elements, tubes or pipes of reinforced plastic can be produced by various methods. Thus, pipes can be produced by centrifual molding, which comprises placing the fabric on the inner wall of a metal tube rotating at high speed, introducing resin into the tube, which penetrates into the fabric, by centrifugal force, and hardening the resin by heating the tube-mold. French Pat. No. 1,347,394 applies this method to the manufacture of a pillar in a conical, slightly inclined mold, while French Pat. No. 2,197,711 uses the same principle to manufacture a conical tube of reinforced synthetic resin.
A second method which is the most widely used consists of winding on a form composed of several disassemblable elements, as proposed in French Pat. No. 1,169,030, or on a mandrel, a filament or ribbon which is passed through a bath of resin for impregnation, as disclosed in French Pat. No. 1,302,187. This method requires constant attention to the impregnation of of the filaments and in general, requires that the filaments be kept under uniform tension, to provide a structure with high mechanical strength.
Another method generally used to manufacture a hollow structure open at both ends, consists of cutting a large number of flongs of fabric, impregnated with resin, corresponding to the form of the desired structure. These fabric flongs are then grouped and stacked in a predetermined order and positioned on a mandrel representative of the interior shape of the structure. The positioned fabric and mandrel are then pressed in a mold formed of two half-shells corresponding to the shape of the structure. The structure can then be polymerized at ambient temperature or in an oven at an elevated temperature and at a temperature dependent upon the nature of the fabric and the resin used. This method of manufacture is time-consuming and expensive. It also results in a substantial waste of fabrics which are high in cost since they are made of threads of silica or threads of carbon or graphite, for example, when used in aeronautical construction.
Particularly in aeronautical structures, the required mechanical strength of the pipes produced by the various methods mentioned above, is not always achieved owing either to poor impregnation of the textile structure before winding or to irregular tension in the course of winding or to the uneven molding pressure in a half-shell mold.